One of the options for "Relationship Status" on Facebook. Refers to a couple in an ambiguous state between "friends" and "in a relationship". May also be used to indicate dissatisfaction with an existing relationship.

If someone changes their status from "In a Relationship" to "It's Complicated", expect them to be "Single" and "Looking for Random Play" soon.

Can also mean a relationship status that does not fit into the status quo, or the options that are available in the chekboxes for forms. A favorite choice that is now available on facebook for people who are in three-way relationships, or other polyamorous relationships including swinging, bisexual openness, and others.

"How do I tell me friends that I am in a relationship with my primary partner, but I am open to intimate adventures with other girls for bisexual threeomes?" I don't want to scare off any potential thirds, but I want to keep all the annoying social network stalkers from hounding me everyday...
Check "it's complicated"

a couple that can't decide to be friends, friends with benefits, or to be in a full out relationship. Friends continue to ask each person what their situation is but no one can truly say in a relationship.